Abstract
Traditionally, inorganic nanoparticles (SiO2, TiO2) have been utilized to tune the optical haze of optoelectronic devices. However, restricted to complex and costly processes for incorporating these nanoparticles, a simple and low-cost approach becomes particularly important. In this work, a simple, effective, and low-cost method was proposed to improve optical haze of transparent cellulose nanofibril films by directly depositing micro-sized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized wood fibers (“coating” method). The obtained films had a high total transmittance of 85% and a high haze of 62%. The film samples also showed a high tensile strength of 80 MPa and excellent thermal stability. Dual sides of the obtained films had different microstructures: one side was extremely smooth (root-mean-square roughness of 6.25 nm), and the other was extremely rough (root-mean-square roughness of 918 nm). As a reference, micro-sized TEMPO-oxidized wood fibers and cellulose nanofibrils were mixed to form a transparent and hazy film (“blending” method). These results show that hazy transparent films prepared using the “coating” method exhibit superior application performances than films prepared using the “blending” method.
Highlights
Tuning optical performances including transparency and optical haze play a critical role in preparing optoelectronic devices with varying optical requirements
The visual appearance of TEMPO-oxidized cellulose nanofibrils (TOCNs) films, TOCNs/TEMPO-oxidized wood fibers (TOWFs)-B films, and TOCNs/TOWFs-C films in close contact with a color pattern is shown in Figure 1a–c, respectively
It can be seen that all the films had high transparency, and the pattern under the transparent films can be clearly observed by human eyes. These results indicated that the existence of TOWFs has a weak influence on the transparency of TOCNs/TOWFs hybrid films
Summary
Tuning optical performances including transparency and optical haze play a critical role in preparing optoelectronic devices with varying optical requirements. Methods for preparing hazy transparent films can be classified into two types: the particle-diffusing type, which relies on the transparent particles inside the transparent films to scatter light, and the surface-relief type, which relies on microstructures on the surface of the transparent films to scatter light [4,5]. For the surface-relief type, polydimethylsiloxane (PDMS) replica molding [8], the silver halide sensitized gelatin method [9], holographic recording [10], the 3D diffuser lithograph [11], photofabrication [12], hot embossing [13], and roller extrusion [4] have been developed to replicate the microstructures onto the surface of plastic films. Most methods employ complex processes and require expensive equipment
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